But that proves too much since even the freewill theist God could give everyone irresistible grace.

Or the freewill theist God could redefine the terms of salvation. Broaden the terms of salvation sufficiently to save everyone. That wouldn't infringe on libertarian freedom. Even the psychopaths could be consigned to an eternal tropical paradise. Kinda like those Swedish "prisons" that resemble resort hotels.

In addition, as James Anderson points out:

It appears to me that your symbolization of Jerry’s premise 5 is incorrect. As you have it, the mere fact that God can give irresistible grace to S entails that S will be saved. But that’s not what premise 5 states or implies, nor is it something that the Calvinist ought to grant.

Rich Davis concedes that objection, but adds:

Here’s another possibility. My symbolization of (5) is what Jerry intends, but there is a supporting argument for (5)–running in the background, as it were–which employs certain bridging premises.

Problem is, Walls and Davis want the benefit of a bridging premise without having to supply a bridging premise. If they have a supporting argument, let's see it! Freewill theists keep giving us I.O.U.s.